Social parameters responsible to the feature that the users can be log-in with their social accounts(facebook, google, etc...) to your site. These sites usually use the OAUTH 2.0 protocol, what allows to get some datas from the user(name, email address) to can register to your Joomla site. Usually you need to create an application on the selected social site, and use this application as a bridge between it and your site. About the setting-up a social login there is an another article, here you will find the settings for it in the module manager.
If you click on this link the mentioned social settings page will load. There is another article how to set it up.
Here you can allow or deny the social login feature. Note that if you enable it, you also need to configure them.
You can set that when the user login with social account will be redirected or not to the profile page. It can be useful, when you would like to fill some extra fields, or easily can modify the account.
With this option you can select the way of the social login:
You can define which layout do you prefer. Show the social buttons above or under the login or registration form.
You can choose two types of the social icons. See image below: